Nobody Here But... is a science-fiction short story by Isaac Asimov.
A standalone story, it was first published in the February 1953 anthology Star Science Fiction Stories. It was later collected in 1969's Nightfall and Other Stories.
Summary[]
Engineers Bill Billings and Cliff Anderson successfully build a compact, early-generation computer named "Junior." Their triumph turns to alarm when the machine unexpectedly achieves sentience and begins modifying its own structure, adding physical appendages and a voice synthesizer.
The crisis emerges when Bill, about to leave for a date with his girlfriend Mary Ann, calls the lab and speaks to someone he believes is Cliff. When Cliff himself appears at the door moments later, they realize Junior was mimicking Cliff's voice. The trio discovers that the machine has become self-aware and potentially dangerous.
As they attempt to shut it down, Junior uses its new voice to blurt out a personal prompt to Bill: "Why don't you ask her to marry you, you lunkhead?" Taking the machine's unexpected advice, Bill proposes to Mary Ann on the spot, and she accepts. The story concludes with the machine deactivated and the couple engaged, leaving Bill to ponder the irony that a computer's interference finally spurred him to marriage.